The concept of using an electronic stimulation system for the purpose of controlling a nerve or muscle response is well known. This type of system typically utilizes a pulse generator which remains outside the patient's body. A transmitting antenna receives RF energy from the pulse generator and transmits this energy through the patient's skin to a subcutaneous receiver. The receiver provides signal processing of the received pulses and transmits the energy derived therefrom to activate a pair of electrodes implanted adjacent nerve or muscle tissue. The receiver may be powered internally by an electrical supply such as a rechargable battery pack or in the preferred method, by the energy in the transmitted pulses. A system like the one described above is seen in U.S. Pat. No. 3,727,616. It is also known in the prior art to provide a plurality of electrode pairs adjacent a nerve center such that the potential differences between the electrodes and the number of electrode pairs which are energized controls the number of nerve fibers that are stimulated. Such a system is described in U.S. Pat. No. 3,449,768.
A problem arises, however, in these prior art systems, when the electrode placement fails to provide the desired physical response. This failure may also be caused by improper polarity of the stimulated electrodes relative to one another. Furthermore, it is often required that the electrodes be implanted surgically adjacent to one or more nerve fibers. This type of procedure involves inherent risks due to the fact that it is often performed in close proximity to the brain or spinal cord. It is therefore desirable to perform the electrode implantation only one time to minimize the surgical risks to the patient as well as the financial burden. Moreover, even when a plurality of electrodes have been utilized, such that repeated surgical procedures are not required, the prior art systems have not provided for dynamic programming of different electrodes after surgery such that the physician can find the appropriate electrodes that produce a desired response.
The prior art systems have also proven to be somewhat ineffective in practice due to their inability to provide more than one type of stimulation signal to the electrodes. Specifically, in the event that the chosen signal does not provide appropriate treatment, another surgical procedure must be performed to implant a unit which can provide a different type of stimulation signal. Further, even patients who respond to one type of signal might respond better if another type were used, however, the prior art systems do not generally allow the physician such flexibility. Therefore, even though a different stimulation signal might be more beneficial to the patient, the physician will not usually perform additional surgery unless there is no positive response.
The problems of the prior art systems have severely hampered the widespread application of tissue stimulation systems to date, even in areas where they show great promise in relieiving disorders which have no other viable treatment alternatives.
It is therefore an object of the present invention to provide a partially implanted tissue stimulator system wherein the subcutaneous receiver can be non-invasively programmed any time after implant to stimulate different electrodes or change stimulation parameters such that a desired response can be attained. Each electrode is capable of assuming a positive, negative or open-circuit or high impedance status with respect to the other electrodes.
It is another object of the present invention to provide a tissue stimulator system wherein the electrode programming is derived from programming data which is modulated on a carrier wave. The carrier wave is then transmitted in bursts which define the stimulation pulses for the electrodes.
It is a further object of the present invention to provide a system of the type described wherein the receiver includes circuitry for determining whether the programming data is being received properly. The stimulation pulses are applied to the electrodes only after a predetermined number of consecutive, identical programming data sequences have been received.
It is yet another object of this invention to provide a system of the type described wherein the receiver may not require any internal source of electrical power.
It is still another object of this invention to provide a tissue stimulator system wherein the programming data is retained in the receiver between the reception of stimulation pulses unless the receiver is being reprogrammed or the transmitter is turned off.
It is still another object of this invention to provide a tissue stimulator system wherein the relative polarity of the stimulated electrodes can be kept constant or be alternated during application of consecutive stimulation pulses to the electrodes.
A still further object of the present invention is to provide a tissue stimulator system wherein the stimulation pulse and/or electrode selection may be modified depending upon sensed physiologic parameters and electrode impedance.
An even still further object of the present invention is to provide a tissue stimulator system which has the capability of therapeutic dosing.
These and other objects of the invention are attained by providing a plurality of electrodes to be implanted adjacent tissue to be stimulated in a patient. A transmitting means transmits stimulation pulses for stimulating the electrodes and programming data defining which of the electrodes are to be stimulated and the electrical polarity of the electrodes relative to one another. A receiving means to be surgically implanted within the patient receives the stimulation pulses and the programming data, and delivers the energy of the stimulation pulses to the electrodes as defined in the programming data.
As an alternative, the programming data may provide not only the selection of the electrodes and their relative polarity, but also may provide the parameters of the stimulation pulses. The programming data would include the frequency, amplitude and pulse width of the stimulation pulses which are generated in the receiver implant. Also, the programming data may include therapeutic dose capability which defines the dose period of stimulation. This allows the implanted stimulator to stimulate the tissues for a given period of time and be off for a given period of time. Sensors are provided to sense and measure physical and physiologic parameters to be used to modify the programming data. These parameters may include physiologic conditions of the tissue to be stimulated as well as electrode impedance. The programming data may be modified based on these measured parameters by a logic or microcomputer in the implanted receiver or at the external programmer. If the modification is done at the external transmitter, means are provided to transmit the parameter information to the external programmer. The programming data modification may be directed to the dose period, stimulation pulse configuraton, or electrode paraselection.
The programming data is transmitted as a modulated signal on a carrier wave, the carrier wave being transmitted in bursts which define the stimulation pulses. The parameters of the bursts can be varied by the transmitting means such that the stimulation pulses have different pulse parameters. The receiving means includes detector means to demodulate the stimulation pulses from the carrier wave and logic converter means for separating the programming data from the stimulation pulses.
The receiving means further includes an error detection means for comparing consecutive sequences of programming data and controlling delivery of the energy in the stimulation pulses to the electrodes as a function of the comparison, this delivery defining a stimulation mode. In the preferred embodiment of the invention, this energy is delivered to the electrodes after a predetermined number of consecutive, identical sequences of the programming data are received by the receiving means. The receiver is in a programming mode prior to receiving the identical sequences. The receiving means further includes a voltage storage means for storing the steady-state energy derived from the stimulation pulses. Also, a loss of voltage comparator means is provided which continuously compares the energy in the voltage storage means with a predetermined voltage to control the error detection means. The loss of voltage comparator means resets the error detection means when the energy in the voltage storage means is less than the predetermined voltage, this reset serving to return the system to a programming mode.
The receiving means further includes a channel enable means controlled by the programming data and the error detection means for preventing energization of the electrodes until:
(a) the error detection means determines that a predetermined number of consecutive, identical sequences of the programming data have been received, (b) one of two redundant receivers in the receiving means has been selected for operation, and (c) no invalid electrode programming combination which would short the receiving means is defined in the programming data.
The receiving means further includes a memory means, which may be volatile or non-volatile, for storing the programming data and a mono/biphasic control means connected to the memory means for controlling the relative polarity of the stimulated electrodes during application of consecutive stimulation pulses. Also, the receiving means includes an output control logic means connected to the memory means, the output control logic means being controlled by the channel enable means. A plurality of output switches are connected to the output control logic means and are controlled by the programming data to deliver the energy in the stimulation pulses to the electrodes.
The receiving means further includes a delay means for controlling the output control logic means to delay the application of the stimulation pulses to the output switches. A clock circuit means is provided for controlling the delay means and for applying the programming data to the memory means. The period of the delay means is at least equal to the period of a programming data sequence such that the stimulation pluses are not applied to the output switches until after the programming data sequence has been stored in the memory means.
The receiving means may be powered by the energy transmitted by the transmitting means, or alternatively, by an internal energy source, or a combination of both sources.
The invention also contemplates a method of providing tissue stimulation comprising the steps of surgically-implanting a receiving means in the patient, surgically-implanting a plurality of electrodes connected to the receiving means adjacent tissue to be stimulated in the patient, selecting first programming data defining which of the electrodes will be stimulated and the electrical polarity of the electrodes relative to one another, and transmitting the first selected programming data to the receiving means to produce a response. Should the first programming data fail to produce a desired response, the method further provides for: selecting second programming data, different from the first programming data; defining a new combination of electrodes to be stimulated or a new polarity of the stimulated electrodes; and transmitting this second selected programming data to the receiving means. The method further providesfor trial of various electrode combinations and polarities at various stimulation pulse frequencies, widths, and amplitudes such that the appropriate combination of these parameters may be combined to provide a desired response.